Analysis of O29 DNA polymerase by partial proteolysis: binding of terminal protein in the double-stranded DNA channel.

o29 DNA polymerase, which belongs to the family of the eukaryotic type DNA polymerases, is able to use two kinds of primers to initiate DNA replication: DNA and terminal protein (TP). By partial proteolysis we have studied the regions of o29 DNA polymerase involved in primer binding. With proteinase K, no change in the proteolytic pattern was observed upon DNA binding, suggesting that it does not induce a global conformational change in o29 DNA polymerase. Conversely, two of the three main cleavage sites obtained by partial digestion of free o29 DNA polymerase with endoproteinase LysC were protected upon DNA binding, indicating that the DNA could be occluding these cleavage sites to the protease either directly by itself and/or indirectly by induction of local conformational changes affecting their exposure. Partial proteolysis with endoproteinase LysC of o29 DNA polymerase/TP heterodimer resulted in a protection and digestion pattern similar to that obtained with DNA, suggesting that both primers, DNA and TP, fit in the same double-stranded DNA-binding channel and protect the same regions of o29 DNA polymerase.